1. Field of the Invention
The present invention relates to an antenna and an antenna module which are used in a radio communication apparatus such as a radio LAN (Local Area Network) and mobile communications, and also relates to a radio communication apparatus provided with the same.
2. Description of the Related Art
A radio communication apparatus such as a radio LAN and mobile communications in recent years has been rapidly made to be small-sized, light-weight, high-performance and capable of high-speed data communication, and an antenna serving as one of the components of the radio communication apparatus has been also strongly desired to be small-sized, high-performance and ready for a wide band.
Among communication systems using the radio communication apparatuses, a wide-band communication system is in the limelight, expected to be usable for an ultrahigh-speed radio communication system in the future, because Federal Communications Commission (abbreviated as FCC) approved general use thereof. In the wide-band communication system, wide-band signals of a very wide frequency band such that used frequencies range from 3.1 GHz to 10.6 GHz are used, and a horn antenna, a discone antenna and the like are thought to be usable in general as the antenna used in the radio communication apparatus in point of wideness of the band and highness of gain.
However, the horn antenna and the discone antenna are of large outer sizes, and on the price side, it is difficult to lower the prices thereof, so that there is a problem such that the antennas become hard to apply to a mobile information terminal or the like, which is a radio communication apparatus for general use.
As opposed to the above, it was proposed to use a monopole antenna in which a radiation electrode having a plate-like shape is opposed to a ground electrode at a taper angle and make the antenna ready for wide-band signals (refer to U.S. Pat. No. 5,828,340, for example).
However, in the case of forming the radiation electrode at a taper angle with the ground electrode in the monopole antenna, the setting of the angle and the setting of the size of the radiation electrode subtly affect radiation characteristics, so that there is a problem such that it is difficult to obtain a stable antenna characteristic.